Planetary lapping machine abrading plates

ABSTRACT

Lapping plates for a double lapping planetary machine are formed of 85 percent AL203 to provide precise dimensional control of workpieces. The top lapping plate is adjustably mounted to float on the workpieces and also permits the introduction of lapping slurry to the workpieces.

United States Patent 1 Lynah, Jr. et a1.

[111 3,744,187 [451 July 10, 1973 PLANETARY LAPPING MACHINE ABRADING PLATES [75] Inventors: Francis P. Lynah, Jr.; Morton J.

Leonard, Jr., both of Carlisle, Pa.

[73] Assignee: P. R. Hoffman Company, Carlisle,

[22] Filed: July 22, 1971 [21] Appl. No.: 165,226

521 U.S.Cl. ..5l/ll8,51/263 51 Int. Cl B24b 7/00 [58] FieldofSearch ..51/111R,117,118,

[5 6] References Cited UNITED STATES PATENTS Borganti 51/161 2,610,451 9/1952 Indge l 51/161 3,063,206 11/1962 Meyerhoff Primary Examiner-Donald G. Kelly Atzomey- Sughrue, Rothwell, Mion, Zinn & Macpeak [5 7] ABSTRACT Lapping plates for a double lapping planetary machine are formed of 85 percent AL 0 to provide precise dimensional control of workpieces. The top lapping plate is adjustably mounted to float on the workpieces and also permits the introduction of lapping slurry to the workpieces.

3 Claims, 3 Drawing Figures PLANETARY LAPPING MACHINE ABRADING PLATES BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is directed to a planetary lapping machine designed for precision lapping of workpieces, and more particularly, to the use of a pair of aluminum oxide lapping workplates for insuring a highly precision sizing and surface finish to the workpieces.

2. Description of the Prior Art Planetary lapping machines that provide double lapping of a workpiece have been available in the prior art from the PR. Hoffman Company of Carlisle, Pa. Generally a lapping machine is a small machine tool which can be used to grind or abrade flat surfaces. The grinding action is accomplished by placing the appropriate workpiece in a properly shaped and located hole in a planetary gear or carrier. The workpiece and the carrier are positioned between two flat plates and propelled in a circular path while applying a mixture of abrasive grain and vehicle. Generally, the flat abrading plates have been cast iron lapping plates. A center hub or sun gear forms the inner boundary of the lapping plate, while an internal ring gear forms the outer boundary. The carriers are in effect planetary gears that are meshed between the sun gear and the ring gear to provide a planetary motion to the workpieces. The gearing arrangement is such that the workpiece will not touch the same spot on the lapping plate in over one thousand revolutions. By use of double lapping plates, equal amounts of materials can be removed from each side of the workpiece and it is possible to develop extreme parallelism. That is, all points on either side of the workpiece are parallel.

Generally the cast iron lapping plates, both top and bottom, were equipped with steel rings on the inside and outside diameters which were recessed slightly below the lapping surface and helped support the periphery of the rotating carriers which extend over the edges of the lap plates. The workpieces were positioned in the carriers in such a way that the work would move partially out over the edges of the lapping surface. This would maintain the flatness of the plates and assure the production of relatively flat and parallel work, as well as removal of chips and used abrasive. With the use of this form of planetary lapping machinery, large quantities of blanks with a high degree of flatness, parallelism and uniformity would be produced, especially on relatively soft workpieces. As a supplemental feature, paper discs could cover the iron lapping plate work surfaces to permit a polishing of work blanks.

Generally, the grinding efficiency, the size and the surface finish can be affected by many variables and the optimization of the grind depends on the proper selection of both hardware and process steps, plus a highly skilled craftsman. Particular problems plague the industry with the introduction of extremely hard workpieces such as ceramics.

It had been found in the prior art that machines that would generate flatness often do not generate parallelism and generally machines that did generate flatness and parallelism could not generate surface finish. Surface finish R. M. S. is the relative freedom of the workpiece surface from both microscopic peaks and valleys. Generally, the optimum conditions'that prevailed in the prior art were realized with planetary lapping machine using pellon paper on stainless steel lapping plates. When using this particular arrangement on the extremely difficult workpieces made of hard ceramic, it was possible to achieve a uniform thickness of 0.00005 inches. with a thickness tolerance of a l or 0.000025 inches, parallelism within 0.00002 inches, flatness within two to four light bands and a surface finish of 5-6 micro inches R. M. S. (root mean square). As an example of the hard ceramic materials which presented great difficulties in lapping is a ceramic including 99.9% AL O SUMMARY OF THE PRESENT INVENTION The present invention provides an improved double lapping plate arrangement for use with a double lapping planetary gear machine. The use of this improved plate system with a standard planetary machine and the proper compounds creates a highly precise parallelism, high surface finish and extreme flatness in one machine operation. The lapping plates of the present invention comprise an 85% AL O work surface with an adjustable mounting fixture. Thus, a modified lapping ma chine with the present invention will economically generate in a single operation the extremely precise parameters on hard ceramic parts that heretofore have been I impossible to achieve.

Actual experiments with X; inch diameter X0.054 inch thick parts of a material such as a 95.5 percent alumina with the lapping machine run at rpm for approximately 25 minutes and diamond lap oil applied to the lapping plate surface produced finished workpieces that were measured to be parallel within 0.000008 inches, flat within one-fourth light band, uniformly thick within 0.00002 and carried a surface finish of 1 micro inch R. M. S. When compared with the best efforts previously achieved in the prior art, it can be seen that the present invention provides a vast improvement in a single abrading operation.

The diamond compound lapping oil was the standard compound available from the Glennel Corporation U.L. 1 micron 5 grams. The initial workpieces consisted of 99.9% AL O varying 0.0005 inches in thickness and run in batches of 50 parts per production unit.

As can be determined from the parameters developed in the prior art, the present invention provides a substantial improvement in the quality of the finished hard ceramic workpieces.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of the double planetary lapping machine with the adjustable top plate removed;

FIG. 2 is elevational exploded view showing the upper lapping workplate and the upper mounting member of the present machine, and

FIG. 3 is a plan view of the upper mounting member and upper workplate, with parts broken away.

BRIEF DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1, a perspective view of the bottom portion of a planetary lapping machine 10 is presented. Basically the planetary lapping machine 10 consists of a lower lapping workplate l2 bounded by a central hub or sun gear 14 and an internal ring gear 16. The work blanks 18 are held in place by a holder or carrier 20 which essentially is a planetary gear having cavities of the same shape as the workpiece 18. A variable speed motor 22 creates a relative motion between the workpiece 18 and the lower lapping workplate l2 and the upper lapping workplate 24 as the carrier 20 rotates about the hub 14.

A timer 26 regulates the length of the production process while a source of lubrication 28 providing lubricating oil to the periphery of the lapping plates, from which it can be carried by the teeth of the carrier 20 across the surface of the lapping plates. As an alternative, the diamond lap oil can be sprayed on the lapping plates 12 and 24 prior to the start of the lapping operation.

Referring to FIG. 2, the top lapping plate of 85% AL O is disclosed. Equally spaced about the surface of the lapping plate 4 are slurry grooves 30 each having 4 equally spaced holes or bores 32 drilled entirely through the lapping plate to permit the slurry to be fed to the grooves and be applied to the contact surface between the lapping plates 12 and 24, and the workpieces 18. The carrier 20, being essentially a planetary gear in an epicyclic gear train, moves the workpiece 18 between the two lapping plates 12 and 24 and a grinding action on the workpiece .18 is carried out by the grains in the slurry lodging in the lapping plates and contacting the workpiece 18. A number of variables exist such as the plate weights, the relative size of the machine parts, the machine speed, the abrasive lubricating oil and slurries, the grinding time, etc.

Referring to FIG. 3, the mounting member 34 for the upper lapping member 24 preferably is made from aluminum or an aluminum alloy and comprises a hub portion 36 having a slightly larger bore diameter than the hub 14. A recessed peripheral groove 38 permits the actual mounting of the upper or top plate lapping member 24.

Three equally spaced mounting pads 40 are bound to the top lapping plate 24 by an epoxy bond. Attached to the pads is a vertically extending stud 42 threaded to receive a mounting nut 44. Appropriate holes in the mounting member 34 permits a vertically adjustable mounting of the top lapping plate 24 in the mounting member 34.

The mounting member 34 is restrained from rotational movement by a bar(not shown) attached to the planetary lapping machine 10. Appropriate apertures 46 permit the introduction of slurry to the slurry grooves 30 in the top plate lapping member 24. The mounting member 34 and the top plate lapping member 24 float on top of the workpieces l8 and are supported by these workpieces 18 as they move in relative contact. By float, the invention implies that the workpieces support the entire weight of the top lapping late.

p A mounting member (not shown) for the lower lapping workplate 12 may have a shape similar to that of the upper mounting member 34, but it does not include holes for the insertion of studs similar to studs 42 because the lower lapping workplate 12 does not include mounting pads, studs, and bolts similar to the mounting pads 40, studs 42, and bolts 44 of the upper lapping member 24. The lower mounting member is also preferably formed of aluminum or an aluminum alloy.

Generally, the machine operator will spray a UL-l micron diamond compound available from the Glennel Corporation onto the aluminum oxide lapping plate surfaces prior to inserting the workpieces. The carriers 20 with the workpieces 18 are then positioned on top of the lower lapping workplate l2 and the adjustable top plate assembly of the mounting member 34 and the top lapping plate 24 are assembled onto the workpieces l8 and clamped into position to prevent rotation. The timer 26 is set to the prescribed time lapse and the double planetary lapping machine 10 is activated to rotate the workpieces 18 relative to the upper and lower lapping plates 12 and 24 respectively. A slurry can be applied through the grooves 30 and the bores or holes 32 to the workpieces 18 while a formula C lapping oil available from the Glennel Corporation can be utilized to control drag. The double planetary lapping machine 10 will stop automatically under the control of the timer 26 and the top plate assembly is then dismantled to permit the workpieces 18 to be removed.

As noted above, the lapping of hard ceramic workpieces has created numerous problems, particularly in the areas of parallelism, flatness and surface defects. Lapping a workpiece on one side only prohibits any control of parallelism and a cast iron double lapping to control the parallelism, will not provide an adequate flatness to the workpiece nor control of the surface finish when dealing with hard ceramic workpieces. By the present invention of double lapping a workpiece on both sides with an percent aluminum oxide lapping plate it is possible to achieve a high degree of parallelism and flatness, with relatively no surface defects, that is, a low root mean square (R. M. S.) surface. The unique use of an aluminum oxide plate of the particular composition as presented in the present invention has permitted the quality production of workpieces to a de-. gree of preciseness that has not been found in the prior art.

While the above description presents the preferred embodiment it should be understood that a skilled craftsman can make numerous modifications within the scope of the present invention, and accordingly, the present invention should be measured in light of the claims and not solely by reference to the previously described preferred embodiment.

What is claimed is: l. A double lapping grinding machine in which a carrier member having slots for workpieces is revolved between an upper and a lower lapping plate, said grinding machine including an upper mounting member having a circular recess adapted to receive said upper lapping plate and an adjustable mounting means for controlling the position of said upper lapping plate in said upper mounting member,

said upper and lower lapping plates being formed of approximately 85% M 0 and said upper lapping plate being adapted to float on top of said workpiece as they abradingly move relative to the surfaces of said lapping plates.

2. A double lapping grinding machine as claimed in claim 1 wherein said adjustable mounting means comprises:

a pad bound to the top of said upper lapping member,

a threaded stub attached to said pad and extending through a hole in said upper mounting member, and a nut.

3. A double lapping grinding machine as claimed in claim 1 wherein the surface of said upper lapping plate furthest from said carrier member has a recess with bores extending from the bottom of said recess through said upper lapping plate, said bores being adapted to pass a lapping compound to said workpieces. 

2. A double lapping grinding machine as claimed in claim 1 wherein said adjustable mounting means comprises: a pad bound to the top of said upper lapping member, a threaded stub attached to said pad and extending through a hole in said upper mounting member, and a nut.
 3. A double lapping grinding machine as claimed in claim 1 wherein the surface of said upper lapping plate furthest from said carrier member has a recess with bores extending from the bottom of said recess through said upper lapping plate, said bores being adapted to pass a lapping compound to said workpieces. 